1. Field of the Invention
The present invention relates to a jet-propulsion watercraft including a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to an oil tank of the jet-propulsion watercraft.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The jet-propulsion personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
In a generalized configuration of the personal watercraft, a straddle-type seat is provided to span between substantially the center portion and the rear portion in the longitudinal direction of the watercraft and an engine is contained in an engine room located beneath the seat and surrounded by a hull and a deck. A crankshaft of the engine projects rearwardly in the longitudinal direction and its rear end is coupled to a pump shaft of the water pump, thereby driving the water jet pump. The engine is a two-cycle engine.
In recent years, the use of a four-cycle engine in place of the two-cycle engine has been contemplated. The use of the four-cycle engine requires an oil tank for reserving engine oil (hereinafter simply referred to as oil).
In the personal watercraft provided with the straddle-type seat, the height of the engine is restricted by the vertical position of the straddle-type seat. Nonetheless, the use of the four-cycle engine in place of the two-cycle engine increases the height of cylinder heads due to its valve mechanism. In addition, since an oil pan for reserving oil is provided below a crankcase, the height of the engine is increased.
Also, the temperature of the exhaust gas is higher in the four-cycle engine than in the two-cycle engine. Therefore, cooling performance of the entire engine, including auxiliary machinery, needs to be enhanced.
Further, in the case of the watercraft, front-and-rear weight balance of the watercraft becomes important so that the watercraft can quickly enter a desired planing state. The oil needs to be smoothly supplied to the engine during the planing state in which an oil circulation amount is increased.
Moreover, in a small watercraft, right-and-left weight balance of the watercraft can be taken into account, because of its small width.